Blow molded bottles made of polyethylene terephthalate (PET) resin (so-called plastic bottles) exhibit many excellent characteristics, and therefore are widely used in many different fields as bottle type containers. These types of containers are typically formed by injection molding a preform into a bottomed cylindrical shape, heating the preform to a temperature at which an expansion effect can be effected, and longitudinally stretching the preform by means of the stretch rod while blowing pressurized air, that is, by means of air blow, into the preform so as to stretch and deform the preform into an expanded shape.
Meanwhile, Patent Literature 1 illustrates an invention relating to a method of blow molding a preform using a liquid instead of air, as the pressurized medium. The molding method of this type may use, as the liquid, beverages, cosmetics, detergent, chemicals or the like, which are to be eventually filled as a content liquid into the final product, to thereby eliminate the filling process, which simplifies the production line.
FIG. 8 is a schematic illustration of a conventional blow molding device for blow molding preforms using a liquid instead of air as the pressurized medium. The main part of this device includes a mold 101 and a blow nozzle 104, and disposed adjacent thereto as annex for feeding the pressurized medium are a pressurized liquid feeding part 122 and a liquid circulating part.
The pressurized liquid feeding part 122 is in the form of a plunger pump, which operates by using, as a power source, a pressurized medium Fp fed via piping P1 from a pressurizing device 121 such as a pressure pump or a compressor, and feeds a pressurized liquid L into the preform 31 having a mouth tubular part 32 tightly fitted onto the tip end portion of the blow nozzle 104, through a feed channel Fs in the interior of the blow nozzle 104 via piping P2 and a magnetic valve V101, so as to form the container 41 by imparting shape to the preform 31 along the shape of the cavity 102 of the mold 101, through longitudinal stretching by means of the stretch rod 108 and stretching into an expanded shape by means of the pressurized liquid L.